Abstract

A new high-silica zeolite, terranovaite, was recently found in cavities of Ferrar dolerites at Mt. Adamson (Northern Victoria Land, Antarctica). The mineral [(Na (sub 4.2) K (sub 0.2) Mg (sub 0.2) Ca (sub 3.7) ) (sub Sigma 8.3) (Al (sub 12.3) Si (sub 67.7) ) (sub Sigma 80.0) O 160 .>29 H 2 O] occurs as globular masses that flake off in transparent lamellae; it has a vitreous luster, white streak, {010} perfect cleavage, and {001} distinct parting. The observed density is 2.13+ or -0.02 g/cm 3 . Optically, it is biaxial positive, with 2V = 65 degrees , alpha = 1.476, beta = 1.478, gamma = 1.483 (all + or -0.002). The orientation is X = c, Y = a, and Z = b. Terranovaite is orthorhombic with a = 9.747(1), b = 23.880(2), c = 20.068(2) Aa and topological symmetry Cmcm. The strongest powder X-ray diffraction lines are (d (Aa), I, hkl): 11.94,40,020; 10.16,65,021,002; 9.04,33,110; 3.79,100,025,240; 3.61,40,153. Terranovaite topology, hitherto unknown in either natural or synthetic zeolites, is characterized by the presence of pentasil chains and of a two-dimensional ten-membered ring channel system. The mineral was named terranovaite after the Italian Antarctic Station at Terranova Bay, Antarctica.

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